This invention relates to an electronic detonator.
An electronic detonator typically includes a timer which is capable of executing a time delay with a degree of accuracy which is not attainable with a pyrotechnic device. This allows for improved blasting and fragmentation of rock.
Various techniques exist for initiating an electronic detonator. In one approach an end of a shock tube is exposed to one or more sensors which are included in a detonator. These sensors, in response to a genuine shock tube event, commence a process for initiating the detonator. A benefit which is associated with the use of a shock tube to initiate a detonator, is that some of the problems associated with traditional wired electronic blasting systems, such as wire breakage or current leakage in harsh environments, are obviated.
One kind of shock tube-initiated, electronic detonator employs a piezoelectric element which, in response to a pressure wave produced upon ignition of a shock tube, generates electrical energy. In a different approach, used for example in a detonator known as the ISKRA-T, electrical energy is produced by a magnetic pulse generator which is operated in response to a pressure wave from a shock tube event.
Although the aforementioned detonators do away with the need for interconnecting conductive wires, their usage is limited in one respect namely that each detonator is programmed under factory conditions with a predetermined delay time. This means that a blasting practitioner must keep in stock a number of different detonators with different time delays to cater for common blasting requirements.
Another drawback which is linked to a detonator which makes use of a magnetic generator is that the quantity of electrical energy which is produced by the generator may be limited and this would restrict the duration of the time delay interval to about 3 seconds (in the case of the ISKRA-T).
South African patent application No. 2010/04911 proposes a shock tube-initiated, electronic detonator system in which delay times are programmable in the field. South African patent application No. 2011/06918 describes the use of a radio frequency identity tag in which RFID techniques are used for communicating with an electronic detonator. The use of an optical communication path to a detonator is described in South African patent application No. 2011/06962. Another approach, disclosed in the specification of South African patent application No. 2009/06891, is to cause a battery to be moved inside a detonator, in response to a shock tube output, to initiate a timer.
A detonator which has an on-board battery, as a power source, inherently has a limited shelf life. The battery does, however, allow for an accurate determination of a relatively long time delay. By way of contrast magnetically and piezo-powered detonators do not have a battery-imposed shelf life limitation but, as noted, are not normally capable of executing a long time delay.
An article entitled “Modelling, Design and Testing of an Electromagnetic Power Generator Optimized for Integration into Shoes” describes an optimised design for a magnetic generator for harvesting power produced during walking. The document is silent on the use of the techniques disclosed therein in a detonator application.
An object of the present invention is to provide an electronic detonator which, at least to some extent in a preferred embodiment, addresses the aforementioned factors.